This invention relates to a document separator of a recirculating document handler which separates and feeds stacked documents on a document loading plate one by one to the exposure location on a platen glass surface, ejects and returns exposed documents from the exposure location to the document loading plate. More particularly this invention relates to a document separator which separate documents to be fed to the exposure location from documents to be returned to the document loading plate after exposure.
Conventionally, a recirculating document handler (RDH) is mounted in a copying machine which is structured so that stacked documents to be fed are loaded on a document plate, sequentially separated one by one by a friction separation means installed on the feed end side of the stacked documents starting at the lowest sheet of the stacked documents, and fed to a predetermined location on a glass surface (platen glass) of the document, and exposed documents are ejected and returned to the document loading plate and stacked on the top of the unfed stacked documents.
In the foregoing circulating document handler it is required to detect the recirculation of documents. Generally, a separator arm (sometimes called sorter arm) is placed on the top of stacked documents on the document loading plate beforehand, and exposed documents are sequentially loaded on the separator arm. When the last document which is directly pressed by the separator arm is fed to the exposure location, the separator arm is removed from the document loading location, and when the last page is returned to the document loading plate and loaded on the top of the exposed stacked documents, the separator presses the top of the stacked documents again.
The separator arm may be installed at the back end of the stacked documents on the document loading plate in the feed direction or on the side of the stacked documents. The side installation type is available for a document conveyor which aligns only one side of stacked documents of various sizes loaded on the document loading plate against one side of the document loading plate which is a reference plane but not suited to a document conveyor which aligns the center of the document width.
A recirculating document handler with a separator arm installed at the back end of documents in the feed direction is indicated in Japanese Patent Examined Publication No. 1981-40338 and U.S. Pat. No. 4,164,347.
When a rotating motor is used to drive the separator arm to place it on the top of stacked documents on the document loading plate, it is difficult to accurately control the motor because, the thickness of stacked documents varies.
In a document circulator indicated in Japanese Patent Laid-Open 1985-83024, by allowing a motor to run for a predetermined time, the separator arm rotates by a drive lever which is integrated with the motor shaft, touches the documents, if any, on the document loading plate, and stops. Then, the motor overloads and locks, and the rotation stops (auto shut off). As documents are sequentially fed and the stacked documents under the separator arm reduce in number, the separator arm moves downward by the weight thereof keeping in contact with the stacked documents. When the stacked documents run out, the separator arm moves down to a cutout space under the document loading plate and stops.
However, when the separator arm touches the stacked documents and stops, the separator arm strongly presses the top surface of the stacked documents and stops by a motor lock, so that the overpressure of the separator arm may cause damage to the documents. When the motor ON time from the contact of the separator arm with the top surface of the documents to the stoppage of the motor is too short, the separator arm may be reversed in rotation and returned to the original location.
When the motor ON time is too long, the paper feed resistance becomes high because the separator arm presses the top surface of the documents by the drive of the motor during document feed, causing paper feed errors, scratches on document surfaces, or soiled document images.
An optimum motor ON time depends on the document paper quality and varies with the number of documents (stacked document thickness), so that it is impossible to set the motor ON time to a predetermined value.